Lipoprotein lipase is the enzyme responsible for hydrolyzing triacylglycerols in the plasma. The site of action has been identified as the lumenal surface of endothelial cells of capillaries in a variety of extra-hepatic tissues. Recently, we provided evidence that this enzyme might also function as a mobilizing enzyme capable of hydrolyzing endogenous triacylglycerols in the heart. As a result, an attempt will be made to characterize and more clearly define the role of lipoprotein lipase in this area.